1. Field of the Invention
The present invention relates to a liquid crystal display apparatus.
2. Description of the Related Art
Generally, the liquid crystal display apparatus has an array substrate, a counter substrate arranged opposite to the array substrate with a gap maintained between these substrates, and a liquid crystal layer held between the array substrate and the counter substrate. The liquid crystal display apparatus is light and thin and consumes but a little power. Therefore, it uses in various apparatuses, as office automation (OA) apparatus, information terminals, clocks and television receivers. If it has thin-film transistors (TFTs) used as switching elements, it can respond to input signals at high speed and can display high-quality images. This is why the liquid crystal display is used as display unit for use in various electronic apparatuses that display a large amount of information, such as portable TV receivers, computers, etc.
In recent years, it is increasingly demanded that images be displayed at high resolution and that the display speed be raised, as information is processed in great quantities. The image resolution is increased by, for example, reducing the sizes of the elements constituting the array substrate that has TFTs as described above. In the vertical aligned mode, i.e., one display mode, the liquid crystal display apparatus can responds to input signals faster than in the conventional twisted nematic (TN) mode. Further, in the vertical aligned mode, any rubbing process that results in defects, for example electrostatic damage, need not be performed.
Particularly, the multi-domain vertical alignment (MVA) mode is widely used in practice, because it is relatively easy to increase the visual angle in this mode. In the MVA mode, a voltage is applied to each pixel that has a projection, thus orienting the liquid crystal molecules in various directions and ultimately improving the symmetry of visual-angle characteristics and suppressing the inversion. In another mode, a negative phase-contrast plate is used, compensating for the visual-angle dependency of the phase difference that the liquid crystal layer when the liquid crystal molecules stand upright, making the layer look black. The contrast visual angle is thereby changed to an appropriate value. In still another mode, an in-plane phase difference is imparted to the negative phase-contrast plate, converting the plate to a biaxial phase-contrast plate, thus compensating for the visual-angle dependency of the polarizing plate, too, and obtaining desirable CR visual-angle characteristics.
Techniques concerning the MVA mode are disclosed in, for example, U.S. Pat. No. 6,724,452 B1. The projection mentioned above is arranged inside the pixel. The local light dissipation or voltage drop resulting from the step defined by this projection reduces the transmittivity of the pixel. Thus, the projection is a factor degrading the quality of image. If the space between any two adjacent pixel electrodes formed in the array substrate is large, the aperture ratio will decrease inevitably reducing the transmissivity. It is therefore desired that the size of the projection and the space between the pixel electrodes be as small as possible, in order to secure high transmittivity and high image contrast. The size of the projection and the space between the pixel electrodes are determined by a tradeoff between optical characteristic and alignment stability.
Recently it is strongly demanded that liquid crystal display apparatuses for use in portable terminals should display high-contrast and high-luminance images. In addition, it is demanded that the liquid crystal display apparatuses should display images at high resolution, as high as 300 ppi or more. The higher the resolution, the smaller the pixel electrodes will be. The surface ratio of the projection to the pixel electrode will markedly increase if the MVA mode is employed. The contrast ratio and the transmittivity will inevitably fall very much. The liquid crystal display apparatus can no longer display images of sufficiently high quality. Accordingly, coexistence with a high-definition which suited the relation of a tradeoff conventionally and acquisition of high transmittivity and high contrast ratio is called for.
The present invention has been made in view of the foregoing. An object of the invention is to provide a high-definition liquid crystal display apparatus that achieves high transmittivity and high contrast ratio.